PROJECT 1 SUMMARY/ABSTRACT Intestinal epithelial cell (IEC) damage by the donor alloreactive T cells causes gastrointestinal (GI) graft-versus-host disease (GVHD) allogeneic bone marrow transplantation (BMT). The host IEC intrinsic mechanisms that enhance their resistance to the damage by the donor alloreactive T cells might have therapeutic potential in GVHD. IEC homeostasis and resistance depends on complex interactions between the metabolic energy substrates and the regulation of transcription and epigenetic chromatin modifications such as histone acetylation. But the mechanisms of IEC resistance and the relevance of metabolic regulation of histone acetylation in reducing the severity of GVHD has heretofore not been studied. In the current cycle, we have demonstrated and published that epigenetic regulation by systemic administration of histone deacetylase inhibitors (HDACi) regulates experimental GVHD and successfully translated it into a proof of concept human trial for prevention of clinical GVHD. Preliminary data generated during this cycle also demonstrate a significant alteration in the IEC energy substrates that are derived from microbial metabolites, specifically the essential short chain fatty acids (SCFA), such as butyrate in the intestinal tissues after allogeneic BMT. Preliminary data also show that butyrate, which is a known HDACi, enhances histone acetylation, modulates IECs sensitivity damage, and regulates GVHD in vivo. But the pathways of sensing and the mechanisms underlying the butyrate-mediated effects are not known. Therefore, in this proposal, we will build on these exciting and novel preliminary observations to explore the interplay between microbial metabolite and the HDAC inhibitor, butyrate, and its effects on epigenomic alterations of the IECs in reducing GI GVHD. Specifically, we will test the central premise that endogenous intestinal microbial metabolite, butyrate, promotes acetylation of intestinal IECs and negatively regulates GI GVHD. We will explore this premise in the following three specific aims: 1. To determine the pathways of sensing microbial metabolite butyrate by the intestinal epithelial cells (IECs) and its impact on GVHD. In this SA we will test the hypothesis that chemo- sensing of the microbial metabolite butyrate by the G-protein coupled receptor 43 (GPCR43) on the intestinal epithelial cells (IECs) will reduce GVHD. 2. To analyze the molecular mechanisms for butyrate mediated resistance of intestinal epithelial cells (IECs) after allogeneic BMT. In this SA we will explore the hypothesis that the cell intrinsic oxidative metabolic state of IECs is critical for the butyrate mediated histone acetylation and epigenetic regulation of IECs resistance against damage after allogeneic. 3. To determine the impact of butyrate administration on GVL. In this SA we will test the hypothesis that administration of butyrate will mitigate inflammation and GVHD but retain sufficient GVL responses.